1. Field of the Invention
The present invention relates to the field of treating biomass to enhance its value or rank. More particularly, the invention concerns a process for the treatment of biomass, especially coal, to efficiently convert the selected feed stock from low rank into a high grade fuel capable of increased heat release per unit of fuel. This is accomplished in part by driving off most on the moisture trapped in low grade coal. The process simultaneously scrubs the coal of pollutants or impurities, many of which are organic volatiles, which are also referred to as by-products.
These by-products are largely combustible and can provide the heat energy required to operate the inventive process after start up in a manner similar to that of a petroleum refinery refining crude oil to produce clean fuels. The removed by-products are recycled into products such as roofing tar, and chemical feed stocks. The organic volatiles are light hydrocarbons that can be used as gaseous fuels, first to power the process after startup, with the remaining organic volatiles being separately processed for other applications. The process further renders the coal into a low smoke generating fuel to make its use more acceptable for domestic purposes such as cooking and home heating. Finally, the inventive process reduces the weight of the coal, which reduces the cost to transport the treated coal to the location where it is burned as fuel.
The process is an energy conservation measure on several different levels. The process increases rank of the coal making it a more effective fuel, removes moisture, uses the by-products removed from the feed stock to power the inventive process, produces treated by-products for other applications such as gaseous fuels that contain more useful energy, and reduces the weight of the coal to reduce energy consumption in transporting the coal to its combustion site. The process also recycles heat to further lower fuel consumption in operating the process The inventive process is principally designed for use with sub-bituminous and lignitic coal, but it is equally applicable to biomass such as wood waste, shells, husks, and other combustible material of organic origin.
2. Description of the Prior Art
Biomass is one of the largest and most readily available energy sources known to man. Biomass is found in immature forms, such as wood, shells, husks and peat. Vast amounts of biomass are also available in the form of lignite, sub-bituminous, bituminous and anthracite coal. Man has been releasing the energy trapped in these materials ever since he discovered and was able to control fire. The inefficient release of these vast energy reserves, however, has resulted in a degradation of the quality of the atmosphere and the environment, and some believe it contributes significantly to global warming. The increasing demand for energy, created by man's insatiable appetite for the products made available by an industrialized society, have created a need to release this energy in a safe, clean and environmentally responsible manner.
It is known to treat coal with the application of heat in a controlled environment to increase its rank. The present invention is actually a significant improvement over Hunt, U.S. Pat. No. 6,447,559. Hunt teaches treating coal in an inert atmosphere to increase its rank. In the present invention, coal is first heated to a temperature of 400° F. in an inert atmosphere to produce coal having only 2-5% moisture, then heated in an inert atmosphere to 1500° F. to produce coal having only 1-2% moisture and a mass reduction of up to 30%, to produce coal having less than 2% moisture and a volatiles content of less than 25%, then cooling the coal in an oxygen-free and dry atmosphere, and finally collecting it.
The prior art preceding Hunt had recognized that heating coal removes moisture and enhances the rank and BTU content of the coal. It was also previously recognized that this pyrolysis activity altered the complex hydrocarbons present in coal to a simpler set of hydrocarbons. This molecular transformation resulted in a more readily combustible coal, but an unstable product. The prior processes took several hours to complete, which made them slow and costly in both capitalization and productions costs. Hunt greatly shortened the processing time of the prior art preceding Hunt.
But Hunt does not recognize either the use of by-products to power the process, or the ability to “farm” a great number of by-products for constructive use outside of the process. Hunt is also a horizontal process, while the present invention is a vertical process that can take advantage at certain points of gravity is moving the coal from one zone to another. Energy conservation is achieved by the present process on multiple levels, and environmental conservation is achieved both in the process facility and by the cleaner burning coal after being processed.